The present invention relates generally to apparatus for stacking booklets or other printed material and more particularly to a stacking apparatus in which a succeeding booklet is piled on top of a preceding booklet.
As used herein, the term "booklet" includes generally flat articles which may have a thickness of several sheets or folds as well as a generally flat article comprising only a single fold or sheet in thickness. In its broader sense, as used herein, the term booklet may also include material which is at least initially devoid of printing or other graphics.
In present day printing plants, booklets are typically delivered from a printing press or a folding machine as a continuous stream of booklets arranged in a shingled fashion, i.e., with the front of a succeeding booklet overlapping the tail of a preceding booklet.
Conventional apparatuses for stacking booklets utilize bottom stacking, i.e., an arrangement in which a succeeding booklet in a stream of shingled booklets is introduced beneath the preceding booklet in the stream, with the first booklet introduced into the stack remaining at the top of the stack as the stack grows. In order to bottom stack shingled booklets, the stream of shingled booklets leaving the printing press or folding machine must first be inverted. This is usually accomplished by moving the stream of shingled booklets along a conveyor belt around a drum in a reverse loop. At the conclusion of the reverse loop, the front of a succeeding booklet underlaps the tail of a preceding booklet.
Although reverse looping devices may be satisfactory for some sizes of booklets, they are not sufficiently versatile to handle all sizes of booklets, especially smaller ones, without mishaps during the inverting procedure and the steps leading up to and following the inverting procedure. For example, the stream of booklets is carried around the inverting drum on a plurality of relatively narrow belts spaced apart from each other in a lateral direction. When a small booklet is carried around the drum, the booklet is carried by a single narrow belt only, rather than by a plurality of laterally spaced belts; and there is a much greater chance that the small booklet will become misaligned than where the booklet is larger and is being carried by a plurality of laterally spaced belts.